The present invention relates to a fixing device for use in an electrophotographic image forming apparatus such as a copier, a laser printer and a facsimile.
In the fixing device, it has been considered to adopt an induction heating type of heat source which offers high thermal conversion efficiency in order to achieve energy saving. Particularly, from view-point of their compact design and high efficiency, attention is focus on the fixing device in which magnetic flux generated by coils is guided to a fixing roller by a core member such as ferrite cores.
This conventional electromagnetic induction heating type of fixing device includes a fixing roller, a pressure roller which comes in contact with the fixing roller to form a nip, and a magnetic flux generation means which is disposed inside of the fixing roller to generate magnetic flux.
The fixing roller generates heat by the magnetic flux from the magnetic flux generation means. The nip holds and transports a recording material carrying an unfixed image so that the unfixed image is melted by the heat and fixed to the recording material (see JP 10-74008A)
The fixing roller includes an outside roller for generating heat by virtue of magnetic flux, an inside roller inserted into the inside of the outside roller, and a regulation member disposed on both ends of the outside roller in order to suppress movement of the outside roller in relation to the inside roller in the axial direction.
In the conventional fixing device, however, an axial length of a contact face of the pressure roller that comes in contact with the outside roller is almost equal to an axial length of the outside roller. Therefore, when the fixing roller and the pressure roller rotate while the pressure roller is in contact (pressurized contact) with the fixing roller, the outside roller of the fixing roller suffers elastic deformation caused by the pressure roller and develops bending deformation during rotation.
Thus, since both ends of the outside roller rotate while developing the bending deformation, stress is generated between both ends of the outside roller and the regulation member, which may cause damage on the ends of the fixing roller.